以给定的概率获取true或false [英] Get true or false with a given probability

问题描述

我试图在c ++中写一个函数，它将基于给定的概率返回true或false。所以，例如，如果给定的概率是0.634，那么63.4％的时间函数将返回true。我试过几个不同的东西，失败了。任何帮助？

I'm trying to write a function in c++ that will return true or false based on a probability given. So, for example if the probability given was 0.634 then, 63.4% of the time the function would return true. I've tried a few different things, and failed. Any help?

推荐答案

如果你想在C ++ 11中做这个，你可以使用它的各种随机数引擎， uniform_real_distribution 提供了一个很好的结果。以下代码演示：

If you'd like to do this in C++11, you can use its various random number engines, combined with the uniform_real_distribution to provide a good result. The following code demonstrates:

#include <random>

std::knuth_b rand_engine;  // replace knuth_b with one of the engines listed below
std::uniform_real_distribution<> uniform_zero_to_one(0.0, 1.0);

bool random_bool_with_prob( double prob )  // probability between 0.0 and 1.0
{
    return uniform_zero_to_one(rand_engine) >= prob;
}

或者，您可以使用 bernoulli_distribution ，它直接给你一个具有指定概率的 bool 。它所需的概率是返回true的概率，因此它正是你需要的：

Alternately, you can use the bernoulli_distribution, which directly gives you a bool with the specified probability. The probability it takes is the probability of returning true, so it is exactly what you need:

#include <random>

std::knuth_b rand_engine;  // replace knuth_b with one of the engines listed below

bool random_bool_with_prob( double prob )  // probability between 0.0 and 1.0
{
    std::bernoulli_distribution d(prob);
    return d(rand_engine);
}

如果你的概率是固定的，那么你可以把它移出函数所以：

If your probability is fixed, then you can move it out of the function like so:

#include <random>

std::knuth_b rand_engine;  // replace knuth_b with one of the engines listed below
std::bernoulli_distribution random_bool_generator( prob );  // replace "prob" with your probability

bool random_bool()
{
    return random_bool_generator( rand_engine );
}

或者如果你想让鸽友静静，你可以将它们绑定在一起： / p>

Or if you want to get fancier still, you can bind them together:

#include <random>
#include <functional>

std::knuth_b rand_engine;  // replace knuth_b with one of the engines listed below
std::bernoulli_distribution random_bool_generator( prob );  // replace "prob" with your probability

auto random_bool = std::bind( random_bool_generator, rand_engine )

// Now call random_bool() to get your random boolean with the specified probability.

您可以将 knuth_b 标准引擎：

• std :: linear_congruential_engine


• std :: mersenne_twister_engine


• std :: subtract_with_carry_engine li>
  

• std::linear_congruential_engine
• std::mersenne_twister_engine
• std::subtract_with_carry_engine

或更多，这是上述的版本，参数化的各种方式。我的参考文献列出了以下内容：

or many more, which are versions of the above, parameterized various ways. My reference lists the following:

• std :: default_random_engine


• std :: minstd_rand0


• std :: minstd_rand


• 
  
• std :: mt19937 > std :: mt19337_64


• std :: ranlux24_base


• std :: ranlux48_base


• std :: ranlux24
  
• std :: ranlux48


• std :: knuth_b

• std::default_random_engine (Implementation defined.)
• std::minstd_rand0
• std::minstd_rand
• std::mt19937
• std::mt19337_64
• std::ranlux24_base
• std::ranlux48_base
• std::ranlux24
• std::ranlux48
• std::knuth_b

如果这还不够，还有一些标准适配器可以进一步扰乱随机数序列：

And if that isn't enough, there are some standard adaptors that can further perturb the random number sequence:

• std :: discard_block_engine 它会每次丢弃指定数量的生成值来调整引擎


• std :: independent_bits_engine ，它使引擎能够产生具有指定位数的随机值。 （对您的特殊需求不重要。）


• std :: shuffle_order_engine 通过排列其生成值的顺序来适应引擎。

• std::discard_block_engine which adapts an engine by discarding a given number of generated values each time.
• std::independent_bits_engine which adapts an engine to produce random values with a specified number of bits. (Not important to your particular need.)
• std::shuffle_order_engine which adapts an engine by permutation of the order of their generated values.

第二个列表中的生成器派生自第一个列表中的基本生成器，具有特定参数，适配器或两者。例如， knuth_b 等效于 shuffle_order_engine< linear_congruential_engine< uint32_t，16807,0,2147483647>，256> ，根据我的参考书。

The generators in the second list are derived from the base generators in the first list, either with specific parameters, adaptors or both. For example, knuth_b is equivalent to shuffle_order_engine< linear_congruential_engine< uint32_t, 16807, 0, 2147483647>, 256>, according to my reference book. (The C++ Standard Library, Second Edition, by Nicolai Josuttis, a great reference work.)

您可以在网上找到更多资讯，包括这篇文章。简介： http://en.wikipedia.org/wiki/C++11 #Extensible_random_number_facility

You can find more information online, including this brief introduction here: http://en.wikipedia.org/wiki/C++11#Extensible_random_number_facility

这里还有更多文档： http://en.cppreference.com/w/cpp/numeric/random

您可能需要修改 rand_engine 上面提供种子。上面的示例使用默认种子。如果你想要不同的种子，请参见cppreference.com如何种子。

You will probably want to modify the declaration of rand_engine above to provide a seed. The example above uses the default seed. See cppreference.com for how to seed it if you want a different seed.

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